CLIP-170/Tubulin-Curved Oligomers Coassemble at Microtubule Ends and Promote Rescues

AbstractBackground: CLIP-170 is a microtubule binding protein specifically located at microtubule plus ends, where it modulates their dynamic properties and their interactions with intracellular organelles. The mechanism by which CLIP-170 is targeted to microtubule ends remains unclear today, as well as its precise effect on microtubule dynamics.Results: We used the N-terminal part of CLIP-170 (named H2), which contains the microtubule binding domains, to investigate how it modulates in vitro microtubule dynamics and structure. We found that H2 primarily promoted rescues (transitions from shrinkage to growth) of microtubules nucleated from pure tubulin and isolated centrosomes, and stimulated microtubule nucleation. Electron cryomicroscopy revealed that H2 induced the formation of tubulin rings in solution and curved oligomers at the extremities of microtubules in assembly conditions.Conclusions: These results suggest that CLIP-170 targets specifically at microtubule plus ends by copolymerizing with tubulin and modulates microtubule nucleation, polymerization, and rescues by the same basic mechanism with tubulin oligomers as intermediates

EB1 regulates microtubule dynamics and tubulin sheet closure in vitro.

International audienceEnd binding 1 (EB1) is a plus-end-tracking protein (+TIP) that localizes to microtubule plus ends where it modulates their dynamics and interactions with intracellular organelles. Although the regulating activity of EB1 on microtubule dynamics has been studied in cells and purified systems, the molecular mechanisms involved in its specific activity are still unclear. Here, we describe how EB1 regulates the dynamics and structure of microtubules assembled from pure tubulin. We found that EB1 stimulates spontaneous nucleation and growth of microtubules, and promotes both catastrophes (transitions from growth to shrinkage) and rescues (reverse events). Electron cryomicroscopy showed that EB1 induces the initial formation of tubulin sheets, which rapidly close into the common 13-protofilament-microtubule architecture. Our results suggest that EB1 favours the lateral association of free tubulin at microtubule-sheet edges, thereby stimulating nucleation, sheet growth and closure. The reduction of sheet length at microtubule growing-ends together with the elimination of stressed microtubule lattices may account for catastrophes. Conversely, occasional binding of EB1 to the microtubule lattice may induce rescues

Wide range local resistance imaging on fragile materials by conducting probe atomic force microscopy in intermittent contact mode

International audienceAn imaging technique associating a slowly intermittent contact mode of atomic force microscopy (AFM) with a home-made multi-purpose resistance sensing device is presented. It aims at extending the widespread resistance measurements classically operated in contact mode AFM to broaden their application fields to soft materials (molecular electronics, biology) and fragile or weakly anchored nano-objects, for which nanoscale electrical characterization is highly demanded and often proves to be a challenging task in contact mode. Compared with the state of the art concerning less aggressive solutions for AFM electrical imaging, our technique brings a significantly wider range of resistance measurement (over 10 decades) without any manual switching, which is a major advantage for the characterization of materials with large on-sample resistance variations. After describing the basics of the set-up, we report on preliminary investigations focused on academic samples of self-assembled monolayers with various thicknesses as a demonstrator of the imaging capabilities of our instrument, from qualitative and semi-quantitative viewpoints. Then two application examples are presented, regarding an organic photovoltaic thin film and an array of individual vertical carbon nanotubes. Both attest the relevance of the technique for the control and optimization of technological processe

Ensconsin/Map7 promotes microtubule growth and centrosome separation in Drosophila neural stem cells.

International audienceThe mitotic spindle is crucial to achieve segregation of sister chromatids. To identify new mitotic spindle assembly regulators, we isolated 855 microtubule-associated proteins (MAPs) from Drosophila melanogaster mitotic or interphasic embryos. Using RNAi, we screened 96 poorly characterized genes in the Drosophila central nervous system to establish their possible role during spindle assembly. We found that Ensconsin/MAP7 mutant neuroblasts display shorter metaphase spindles, a defect caused by a reduced microtubule polymerization rate and enhanced by centrosome ablation. In agreement with a direct effect in regulating spindle length, Ensconsin overexpression triggered an increase in spindle length in S2 cells, whereas purified Ensconsin stimulated microtubule polymerization in vitro. Interestingly, ensc-null mutant flies also display defective centrosome separation and positioning during interphase, a phenotype also detected in kinesin-1 mutants. Collectively, our results suggest that Ensconsin cooperates with its binding partner Kinesin-1 during interphase to trigger centrosome separation. In addition, Ensconsin promotes microtubule polymerization during mitosis to control spindle length independent of Kinesin-1

Wafer-scale detachable monocrystalline Germanium nanomembranes for the growth of III-V materials and substrate reuse

Germanium (Ge) is increasingly used as a substrate for high-performance optoelectronic, photovoltaic, and electronic devices. These devices are usually grown on thick and rigid Ge substrates manufactured by classical wafering techniques. Nanomembranes (NMs) provide an alternative to this approach while offering wafer-scale lateral dimensions, weight reduction, limitation of waste, and cost effectiveness. Herein, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process, which consists of the fabrication of wafer-scale detachable monocrystalline Ge NMs on porous Ge (PGe) and substrate reuse. We demonstrate monocrystalline Ge NMs with surface roughness below 1 nm on top of nanoengineered void layer enabling layer detachment. Furthermore, these Ge NMs exhibit compatibility with the growth of III-V materials. High-resolution transmission electron microscopy (HRTEM) characterization shows Ge NMs crystallinity and high-resolution X-ray diffraction (HRXRD) reciprocal space mapping endorses high-quality GaAs layers. Finally, we demonstrate the chemical reconditioning process of the Ge substrate, allowing its reuse, to produce multiple free-standing NMs from a single parent wafer. The PEELER process significantly reduces the consumption of Ge during the fabrication process which paves the way for a new generation of low-cost flexible optoelectronics devices.Comment: 17 pages and 6 figures along with 3 figures in supporting informatio

Nouvelles raisons d’agir des acteurs de la pêche et de l’agriculture

Les acteurs de la pêche et de l’agriculture (professionnels, institutions d'enseignement, techniciens, organisations professionnelles et syndicales, politiques et législateurs, chercheurs, consommateurs…) font l'expérience de l’évolution des techniques et des droits à produire et à prélever la ressource vivante. Les agriculteurs et les pêcheurs se questionnent sur les raisons de faire leur métier, de s’y maintenir et de le transformer par de nouveaux modes de transmission, de débat et par de nouvelles solidarités. Les auteurs, des chercheurs en sciences sociales et des professionnels des deux filières, examinent les situations les plus propices au développement de nouvelles raisons d'agir et de nouveaux savoirs : débats sur la gestion des ressources renouvelables, décisions relatives au contenu du métier et à sa transmission, mutations professionnelles ou encore nouvelle division du travail. Les situations présentées permettent un éclairage contrasté des secteurs de la pêche et de l'agriculture, et plus particulièrement : – de l’évolution des raisons d’agir et des savoirs des professionnels, des scientifiques, des législateurs mais aussi des nouveaux arrivants, notamment dans leur rapport à l’écologie. Comment de nouvelles raisons d’agir et de nouveaux savoirs émergent-ils des divisions et des conflits ? – des transformations du travail et de la formation professionnelle dans les deux secteurs. Comment les référentiels de formation et les pratiques didactiques modifient-ils les enjeux cognitifs, environnementaux, économiques et sociaux des activités de pêche et d’agriculture ? Ces questions majeures intéresseront à la fois les pêcheurs et les agriculteurs, les concepteurs de politiques publiques et les scientifiques

Apports de la cryo-microscopie électronique à l'étude de la structure des microtubules

Nom de l'équipe en 2003 : Structure et Dynamique du Cytosquelette (SDC)International audienc

Cryo-electron microscopy of microtubular assemblies.

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The microtubule lattice ‐ a brief historical perspective

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Segmentation of fibers in cryo-electron tomograms.

PosterNational audienc